French Pat. No. 2 469 273 describes such a press which comprises a central wheel fixed on a rotating shaft driven at a slow speed and rotating inside an eccentric rotating ring having an inside diameter which is larger than the outside diameter of the wheel, thereby constituting a rotary assembly of two cylinders which meet tangentially internally. The outer ring is thrust radially against the outside surface of the wheel by a thrust device which, for example, may comprise rollers mounted on a bogie which is thrust against the outside surface of the ring by a jack or the like which connects the bogie to the wheel's drive shaft. One of the pressure surfaces, e.g. the inside surface of the ring, is perforated to extract the juice.
When it is desired to use a press of this type for pressing a material such as beet pulp which is both slippery and highly deformable and which has substantially no strength in shear or in tension, several major difficulties are encountered. In particular, once the material between the wheel and the ring is subjected to a relatively low pressure, the pulp is extruded through the perforations in the inside surface of the ring, and the perforations rapidly become clogged. Also, considerable flow is observed in the material which escapes sideways from the region of pressure between the wheel and the ring, and is thus not properly pressed. Further, the slippery and sometimes even slimy structure of the pulp limits the transmission of rotating force from the wheel to the ring, which is thus not properly driven.
Beet pulp is a by-product of the sugar extraction process applied in a sugar works to sugar-beet cossettes. The residual pulp is essentially constituted by water, and contains only about 6% by weight dry matter.
When this pulp is fed immediately to animals, it is usually subjected to an initial pressing operattion to bring the dry matter content up to about 10%. If the pulp is to be made into silage for winter storage, it is necessary to proceed with a second pressing operation to obtain about 20% dry matter content. When the pulp is to be transported or included in animal feed concentrates, the dry matter content must be raised to about 85%, which is usually done in two stages: a first stage which consists in tightening up the second pressing operation to obtain up to 25% dry matter on average; and a second stage consisting in dehydration by heating in a drier which is heated by burning heating fuel. The energy expended in this second stage is very expensive.
Preferred embodiments of the present invention enable said expense to be considerably reduced by increasing the dry matter content of the material to be dehydrated. This is done by a particularly effective pressing operation.